The invention discloses a fabrication method for a surrounding gate silicon nanowire transistor with air as spacers. The method comprises: performing isolation, and depositing a material A which has a higher etch selectivity ratio with respect to Si; performing photolithography to define a Fin hard mask; etching the material A to form the Fin hard mask; performing source and drain implantation; performing photolithography to define a channel region and large source/drain regions; forming the Si Fin and the large source/drains; removing the hard mask of the material A; forming a nanowire; etching the SiO2 to form a floating nanowire; forming a gate oxide layer; depositing a polysilicon; performing polysilicon injection; performing annealing to activate dopants; etching the polysilicon; depositing SiN; performing photolithography to define a gate pattern; etching the SiN and the polysilicon to form the gate pattern; separating the gate and the source/drain with a space in between filled with air; depositing SiO2 to form air sidewalls; performing annealing to densify the SiO2 layer; using subsequent processes to complete the device fabrication. The invention is compatible with the CMOS process flow. The introduction of the air sidewalls can effectively reduce the parasitic capacitance of the device, and improve the transient response of the device, so that the method is applicable for a logic circuit with high performance.